The invention relates to an operating boosting device for a motor vehicle clutch having a pedal which is under the effect of a prestressed tension spring which has one end pivotably connected to a fixed point on the vehicle and another end pivotably connected to a pressure rod which is disposed on a lever arm of the pedal. The tension spring exercises a restoring force holding the pedal in an engaged clutch position and during a clutch disengaging operation and after a dead-center position of the clutch pedal is exceeded, supplies a force boosting the clutch disengagement force of the driver's foot. In DE-AS 11 52 896, an operating device for motor vehicle clutches is known where the pedal is under the effect of a restressed tension spring which, according to the position of the pedal, causes a boost of force through a pressure rod. When the clutch pedal is in an engaged clutch position, the spring exercises a restoring force which holds the pedal in this position. When the pedal is operated, as well as when a dead-center position is exceeded, the spring supplies a force which boosts the force of the foot. The pressure rod has one end fixed with the spring at the vehicle body separated by a relatively large distance from the front bearing point of the pressure rod of the pedal. The swivelling angle of the pedal is relatively large, and a boost of force is obtained because the resulting lever arm rises only slightly after the dead-center position is exceeded. It is an object of the invention to provide an operating device of the above type which causes a steep rise of the boost of force after the dead-center position is exceeded.
According to the invention, this object is achieved by having an action line of the force of the boosting spring extend through the fixed point of the tension spring on the vehicle and through the bearing point of the pressure rod during all pedal positions.
It is also advantageous if the pressure rod is pivotably connected to the lever arm at a bearing point which is arranged at the shortest possible distance with respect to the fixed point mounting the tension spring, during the pedal position corresponding to an engaged clutch position. This shortest distance corresponds to approximately half the width of the lever arm. The pressure rod is U-shaped with the legs that carry the bearings point and the connection of the spring to the rod, respectively.
The principal advantages achieved by the invention are that the stored spring force from the booster tension spring will act upon the clutch pedal as a boosting moment particularly at the time it is operated. After the clutch pedal passes a dead-center position, this boost provides a steep response behavior. The response is achieved by the arrangement of the bearing point of the pressure rod and the tension spring. Thus, the pressure rod can be swivelled around the bearing point on the lever arm of the pedal and the spring can be swivelled with the pressure rod around its fixed point on the vehicle. Even if the swivelling angle of the pedal is small, the arrangement advantageously causes an abruptly rising boosting moment. This effect is increased by having the bearing point of the pressure rod at the lever arm and the fixed point of the tension spring at the vehicle body arranged at the shortest possible distance from one another in a clutch engaged position. This causes the action line of force, the course of which is determined by the position of the bearing point and the pivot point of the clutch pedal, to form a larger lever arm as a result of the swivelling angle of the pedal.
By this arrangement, a fast response behavior is achieved with a steeply rising boosting moment to provide for good clutch synchronizing possibilities and at the same time it requires only a few simple components.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.